1. Field of the Invention
The invention relates to a self-propelled construction machine, in particular a road milling machine, which has a machine frame and a milling drum housing, inside which a milling drum is arranged. In addition, the invention relates to a method for operating a self-propelled construction machine.
2. Description of the Prior Art
Known road milling machines have a milling drum, with which the material is milled off. The milling drum is arranged inside a milling drum housing, inside which the milled material collects.
The road milling machines have a conveying device, which takes the milled material away from the drum housing in order to load the material onto a transportation vehicle. In addition, the road milling machines have a scraping device, which is provided behind the milling drum in the direction of work. The scraping device has a height-adjustable scraper blade. If the milled material is to be loaded during the work, the lower edge of the scraper blade skims over the milled surface such that the surface is removed cleanly. In the process the scraper blade shuts the milling drum housing behind the milling drum in the direction of work.
If, on the other hand, it is not intended for the milled material to be loaded, it is necessary to raise the scraper blade in relation to the milling drum so that the milled material can remain behind the milling drum housing in the direction of work. Because of the loosening factor, which is approximately 1.2-1.5, the volume of the milled material increases such that the milled channel can only accommodate part of the milled material. The rest of the milled material is thrown out into a heap, which takes on an angle of friction of approximately 30 to 40° at least on the outer flanks. The height of the heap depends inter alia on the depth of milling and the actual loosening factor that occurs.
If the scraper blade has too low a height in this operating mode, the milled material is retained in the milling drum housing such that the milling drum housing fills increasingly with material, which generates additional friction as a result of which the performance is reduced, the wear is increased, and not least it results in higher fuel consumption. On the other hand, the scraper blade cannot be raised arbitrarily either, since otherwise the milling drum housing would be open behind the milling drum in the direction of work as a result of which the milled material does not remain in the milled track in the desired form of a swathe, but rather is spread widely, leading to time-consuming work afterwards.
In practice, the machine operator is forced to move the scraper blade to a relatively wide open position, since he does not have the chance to examine the relevant region in order to adjust the height of the scraper blade precisely due to the arrangement of the individual components of the machine.
Stabilisers and recyclers do not have a conveying device. Therefore, the drum flap of stabilisers and recyclers, which shuts the drum housing, has to be adjusted such that the material can come out of the drum housing.
The object of the invention is to create a self-propelled construction machine, in particular a road milling machine, which can also be operated if the milled material is not loaded but rather is to remain in the milled track. Another object of the invention is to disclose a method for operating a self-propelled construction machine, if the milled material is not loaded but rather remains in the milled track.
These objects are achieved according to the invention with the features of the independent claims. The dependent claims relate to preferred embodiments of the invention.
The construction machine according to the invention, in particular a road milling machine, has a drive unit with which the scraper blade of the scraper device is height-adjustable in relation to the milling drum. In addition, the construction machine according to the invention has a control and/or regulator unit for the drive unit to adjust the height of the scraper blade and a measurement device to measure the distance between at least one reference point, which relates to the lower edge of the scraper blade, and the milled material.
The control and/or regulator unit of the construction machine according to the invention is designed such that the height of the scraper blade is adjusted depending on the height of the milled material remaining in the milled track. The control and/or regulator unit ensures that, on the one hand, the milled material can come out of the milling drum housing behind the milling drum in the direction of work largely unhindered and, on the other hand, the milling drum housing is largely shut above the material coming out of it. Thus, on the one hand, trouble-free operation of the milling machine is ensured and, on the other hand, a clean result of the work is achieved.
In particular, the self-propelled construction machine is a road milling machine, which has a conveying device in particular to convey the milled material from the milling drum housing to a transportation vehicle. The road milling machine can be a front-loader road milling machine, in which case the milled material is loaded via the front of the machine onto an HGV driving in front of it, or a rear-loader road milling machine, in which case the milled material is loaded via the rear onto a heavy goods vehicle (HGV) driving behind it.
A preferred embodiment of the road milling machine provides for an input unit with which two operating modes can be specified. In the process the design of the input unit is irrelevant. For example, the input unit can comprise one or more switches or buttons. It can, however, also be part of a menu navigation system. In the first operating mode, the conveying device is activated and the control and/or regulator unit is deactivated. This is the case if the milled material is to be loaded. If the milled material is not to be loaded, however, but rather is to remain in the milled track, the second operating mode is specified, in which the conveying device is deactivated and the control and/or regulator unit is activated.
A preferred embodiment provides for the control and/or regulator unit to control or regulate the drive unit in such a way that the measured distance between at least one reference point, which relates to the lower edge of the scraper blade, and the milled material corresponds to a specified value or lies within a specified value range. In practice, it is sufficient if a height correction is only performed when the measured distance leaves a specified tolerance range such that corrections to the height setting of the scraper blade are not being performed constantly.
In order to measure the distance between at least one reference point, which relates to the lower edge of the scraper blade, and the milled material, one or more distance measurements can be performed. The distance measurement can relate to one small measurement point (spot measurement) or a larger measurement region (regional measurement) on the surface of the milled material.
The measurement device is preferably designed such that one or more distance measurements are performed outside the milling drum housing behind the scraper blade in the direction of work. In principle, it is also possible, however, to measure the distance inside the milling drum housing.
The measurement device preferably has one or more distance sensors, which are preferably arranged on the rear side of the scraper blade in the direction of work above its lower edge. The distance sensors can be designed in different ways. They can measure the distance in a contactless or tactile manner. For example, the contactless distance sensors can be known ultrasonic distance measurement sensors, inductive, capacitive, optical distance measurement sensors or radar distance measurement sensors. Tactile distance sensors have at least one tactile element, which rests on the milled material.
In the case of a preferred embodiment, the measurement device is designed in such a way that the distance between the surface of the milled material and a reference point, which is not at the height of the lower edge of the scraper blade, is measured with the distance sensor so that the distance sensor does not have to be located directly on or near the lower edge of the scraper blade. A large scope for the arrangement of the distance sensor is thereby created.
In a sectional plane running transverse to the direction of work, the material thrown out behind the milling drum in the direction of work has a characteristic cross section that depends inter alia on the type of milling drum. Milling drums are known, which are characterised in that the material is thrown out in the center of the milling drum housing such that the maximum height of the material that has been thrown out is at its greatest in a region that is roughly central between the left and right-hand edges of the scraper blade and the height of the material falls away towards the sides. It is, however, also possible, for example, for the material to be conveyed inside the milling drum housing to one of the two sides, a cone of rubble again forming, which then lies on the left or right side, however.
In the simplest case, the control and/or regulator provides for the scraper blade to be located above the highest point of the material that is thrown out, it being possible for said point to be at the center or on the right or left side of the milling drum housing depending on the cross section of the material that is thrown out. The remaining gap between the lower edge of the blade and the upper side of the material should then be as small as possible. It is, however, also possible for the control and/or regulator to intentionally provide for the scraper blade to dip into the material at the highest point if the distance between the lower edge of the blade and upper side of the material is not measured at the highest point.
In a preferred embodiment, the measurement device to measure the distance between the lower edge of the scraper blade and the milled material is designed such that the distance measurements are performed at a plurality of reference points, which are located between the left and right-hand edges of the scraper blade in the direction of work. One embodiment provides for the height of the scraper blade to be adjusted depending on the mean value of the measured distances between the respective reference points, which relate to the lower edge of the scraper blade, and the milled material.
A particularly preferred embodiment provides for the height of the scraper blade to be adjusted depending on the smallest or largest measured distance between a reference point, which relates to the lower edge of the scraper blade, and the milled material. If the height of the scraper blade is adjusted depending on the greatest distance, the scraper blade dips deeper into the material at the highest point whereas in the case of the adjustment of the height of the scraper blade depending on the smallest distance, a gap may even remain between the scraper blade and the material.
The type of distance sensor with which the measurement is to be performed can be selected by the vehicle operator. For example, the vehicle operator may select a central distance sensor that measures the smallest distance for the type of milling drum that throws the material out in the center. The selection of the distance sensor can, however, be undertaken by the control and/or regulator unit itself in that during the measurement of the distance, the sensor with which the currently smallest or largest distance is being measured is always used for control/regulation.
If the material that is thrown out has a symmetrical cross section, for example, a particularly preferred embodiment provides for a central measurement in a region that is preferably 50%, in particular 30% of the width of the scraper blade such that a gap remains between the scraper blade and the material.
In the case of a symmetrical cross section, an alternative embodiment provides for the control and/or regulation to be performed in such a way that the scraper blade dips into the material that is thrown out such that the milling drum housing is completely shut behind the milling drum in the direction of work. The scraper blade must not be allowed to dip too deep into the material in the process, however, since otherwise the material would remain inside the milling drum housing. An ideal adjustment is therefore only given when the scraper blade only dips slightly into the center of the material that is thrown out.
The measurement device in this alternative embodiment is designed such that when the cross section is symmetrical, at least one distance measurement is performed at a specified distance to the left-hand edge of the scraper blade in the direction of work and/or at least one distance measurement is performed at a specified distance to the right-hand edge of the scraper blade in the direction of work. The height of the lateral flanks of the material that is thrown out can be determined using these distance measurements. This height is always lower than the height at the center of the material that is thrown out between the left and right-hand edges of the scraper element. For example, the lower edge of the scraper blade can be adjusted to the height of a point on the left and/or right flanks of the material that is thrown out. In this case, the lower edge of the scraper blade dips at the center slightly into the material that has been thrown out.
The specified distance from the left-hand edge and the specified distance from the right-hand edge of the scraper blade can for example be between 0 and 30%, preferably 10 to 20% of the width of the scraper blade, i.e. of the distance between its left and right-hand edges, since the characteristic extension of the flanks occurs here.